Nybelinia aequidentata ( Shipley & Hornell, 1906 ) Dollfus, 1930

Palm, Harry Wilhelm & Haseli, Mohammad, 2023, Tentaculariids (Cestoda, Trypanorhyncha) of elasmobranchs from Malaysian Borneo, Zoosystema 45 (18), pp. 513-529 : 522-524

Nybelinia aequidentata ( Shipley & Hornell, 1906) Dollfus, 1930

( Fig. 4A, B )

Tetrarhynchus equidentatus Shipley & Hornell, 1906: 83 .

Nybelinia aequidentata – Dollfus 1930: 210.

MATERIAL EXAMINED. — Malaysia • 5 specimens; from Rhinoptera jayakari Boulenger (BO-83) ( Myliobatiformes : Rhinopteridae ); Malaysian Borneo, off Sabah, Semporna fish market; 04°28’44.09”N, 118°37’00.57”E; LRP 4375 -4378, 11002 • 1 specimen; same data; ZMB E. 7713 • 1 specimen; from Maculabatis pastinacoides (Bleeker) (BO-76) ( Myliobatiformes : Dasyatidae ); Malaysian Borneo, off Sabah, Kampung Tetabuan ; 06°01’10.32”N, 117°42’14.76”E; ZMB E. 7712.

MEASUREMENTS

Long worms, 7850-11 776 (10 154, N=4) long. Scolex 2411- 3271 (2867, N =5) long; scolex width 841-1121 (979, N =4, n =11) at level of pars bothrialis, 518-1147 (816, N =5, n=1) at level of pars vaginalis, 744-1128 (947, N =5, n=10) at level of pars bulbosa. Bothria 1287-1415 (1358, N =3, n=5) long. Pars bothrialis 1342-1433 (1391, N =5) long; pars vaginalis 854-1464 (1174, N =5) long; tentacle sheaths 75-121 (92, N= 5, n = 13) in diameter. Pars bulbosa 884-1013 (947, N= 5) long; bulbs 793-982 (900, N =5, n= 10) long, 183- 232 (202, N=4, n= 8) wide, bulb width: length ratio 1.0: 3.7-5.4 (4.5, N =4, n=8); pars post-bulbosa present, 42-67 (54, N =5) long. Velum very lobate in its posterior margin ( Fig. 4A ), 43-537 (400, N= 5, n= 11) long. Scolex ratio (pars bulbosa: pars bothrialis: pars vaginalis) 1.0: 1.4-1.6: 1.0- 1.5 (1.0: 1.5: 1.2, N=5).

Tentacles 1726-2025 (1871, N =3, n= 3) long with 37-43 (39, N =2, n=4) rows of hooks; tentacle width 51-97 (76, N= 5, n = 7) at level of basal region and 69-97 (80, N = 5, n=8) at level of metabasal region. Metabasal armature homeoacanthous, homeomorphous ( Fig. 4B ); characteristic basal armature absent. Basal hooks 8-21 (15, N=5, n =10) long, base 5-12 (9, N=5, n=10) long. Metabasal hooks 30-43 (36, N =5, n= 19) long, base 10-18 (14, N =5, n= 19) long. Number of hooks per half spiral row in basal and metabasal region of tentacle 7 (N= 3, n=5).

Anterior-most immature proglottid 12-18 (15, N =4, n=4) long, 640-1006 (809, N = 4, n = 4) wide; posterior-most proglottid 165-317 (239, N= 4, n =4) long, 598-769 (683, N= 4, n=4) wide.

REMARKS

Historically, Shipley & Hornell (1906) described this species as Tetrarhynchus equidentatus Shipley & Hornell, 1906 from Brevitrygon walga (Müller & Henle) (therein referred as Himantura walga ) off Sri Lanka. After Pintner (1927) redescribed the type, it was transferred to Nybelinia by Dollfus (1930). Wenchuan et al. (1995) reported N. aequidentata from Hemitrygon akajei (Müller & Henle) (therein referred as Dasyatis akajei ) from the Taiwan Strait (see also Wenchuan 2007). Palm (1999) redescribed a plerocercoid of this species from Lepturacanthus savala (Cuvier) , off Sagar Island, Bay of Bengal. Palm & Beveridge (2002) presented measurements of a postlarva as N. aequidentata isolated from Dendrochirus zebra (Cuvier) off New Caledonia (see also Beveridge et al. 2014). Nonetheless, Palm (2004) stated that the specimens identified and described as N. aequidentata by Palm & Beveridge (2002) were synonymous with N. syngenes (Pintner, 1928) Dollfus, 1930 , based on the hook sizes and the length of the bulbs. In the present study, five specimens were collected from Rhinoptera jayakari (BO-83) off Malaysian Borneo. Rhinoptera jayakari is a new host record for N. aequidentata and a new locality record is also established for this parasite off Malaysian Borneo. Although the examined material was strobilate, the internal organs were invisible and we missed the opportunity to describe the proglottid anatomy of this species.

Nybelinia aequidentata most closely resembles N. syngenes , both of which are characterized by a large scolex size, the large metabasal falcate hooks decreasing in size towards the apical and basal regions of tentacle, and the overlapping measurements of the scolex. Despite the fact that N. aequidentata is distinguished from N. syngenes by its acraspedote, rather than craspedote, proglottids, identifying the plerocercoids of these two species is very difficult solely relying on scolex morphology and hook shape. Palm & Bray (2014: 299, plate III) provided a photograph of the scolex of the type of N. aequidentata , in which the velum is very lobate in its posterior margin, a character obviously overlooked in earlier treatments of this taxon. The velum in all our specimens off Malaysian Borneo was also very lobate ( Fig. 4A ). Therefore, the lobate velum and the acraspedote proglottids are the two main characters distinguishing N. aequidentata from N. syngenes . It is of note that the lobate velum was only described in the adults and that it cannot be clarified so far if it is also characteristic for larvae. Nonetheless, the scolex morphology of trypanorhynchs is usually the same in transition from the larval to the adult stage (see Palm 2004) and hence we herein reidentify the postlarval specimen identified by Palm (1999) as N. aequidentata , lacking the lobate velum, with N. syngenes .

Given that the type material of N. syngenes is not known, there is no information on the number of hook rows along its tentacle and from this point of view, it is currently not possible to distinguish N. aequidentata (37-43 hook rows along the tentacle in our specimens from Malaysian Borneo) from N. syngenes .

UNIDENTIFIED MATERIAL

The following material was examined but was unable to be assigned to a species of Nybelinia : 2 specimens (ZMB E. 7714, 7715) from Chiloscyllium punctatum Müller & Henle (BO-282) ( Orectolobiformes : Hemiscylliidae ) off Mukah, Sarawak, Malaysian Borneo (02°53’52.16”N, 112°05’44.12”E); 1 specimen (LRP 11003) from Carcharhinus sealei (Pietschmann) (BO-55) ( Carcharhiniformes : Carcharhinidae ) off Mukah, Sarawak, Malaysian Borneo (02°53’52.16”N, 112°05’44.12”E); 1 specimen (LRP 11004) from Carcharhinus sorrah (Müller & Henle) (BO-70) off Mukah, Sarawak, Malaysian Borneo (02°53’52.16”N, 112°05’44.12”E).

Figures

FIG. 4. — Nybelinia aequidentata: A, scolex with lobate velum; B, basal (left illustration) towards metabasal armature of a tentacle cut in two parts, bothrial sur- face. Scale bars: A, 500 µm; B, 100 µm.